Silicon carbide (SiC) power devices offer better high temperature and much higher electric breakdown performance have drawn much attention recently. Either used singly or used in combination with other non-oxide semiconductor layers such as gallium nitride (GaN) to enhance the power device performance, are common practice in devices fabrication. The first step for such devices fabrication is to prepare a clean, flat semiconductor surface such that the fabrication process can proceed further or to recover the mis-processed surface so that the desired process can be repeated and continued. The flat SiC surface can be prepared, for example, by a chemical-mechanical polishing (CMP) process. U.S. Pat. Nos. 7,998,866 and 7,678,700 teach how water soluble oxidizers can effectively polish SiC in the presence of abrasive particles dispersed in water. While effective, the art did not address the potential toxic waste and tool staining issues that may cause during process, by the best of the proposed chemical-mechanical polishing slurry compositions. In particular, oxidizers such as permanganate, chromate, and ammonium cerium nitrate, which are the key components in the prior art, for examples, are toxic to the environment as well as causing staining to the CMP tool parts, when in close contact with the tools during polishing operation. The most obvious staining occurs on the lapping pads, resulting in dark markings that requires frequent and tedious acid cleaning. Chromate is a biohazard, see Bioremediation of Heavy Metal Toxicity—With Special Reference To Chromium, S. Ray and M. K. Ray, Al Ameen, J. Med. Sci. (2009) 2 (2) Special: 57-63. Manganese salts are toxic and known neuron toxin, see Manganese in Drinking-water, background document for development of WHO Guidelines for Drinking-water Quality, 2011. U.S. Pat. No. 8,557,133 teaches a different approach by using dichromate or permanganate indirectly, to generate soft particles as accelerator to enhance SiC removal during CMP. In another US Patent application, U.S. 2008/0305718, showed how the chlorite, chlorate, and perchlorate salts tested that failed to achieve significant SiC removal during CMP, under the published test conditions. In yet another patent, U.S. Pat. No. 8,247,328, the inventors showed that how the oxidizer-based SiC polishing slurries can be further improved by adding significant amounts of heavy metal catalysts, such as cobalt or platinum, to enhance SiC removal. By doing so the slurries would become even more toxic and more expensive, because of the presence of the extra added heavy and noble metals in the products.
Thus, it is therefore desirable to have a need for alternative CMP formulations that uses no heavy metal-containing oxidizers, produces less staining to the tool, cost effective, requiring no special waste treatment after use, and yet delivers good SiC CMP polishing performance.